Stephen Hawking was 21 years old when he was diagnosed with motor neuron disease, a rare form of ALS.
Doctors told him he would only live for a few years.
More than 50 years later, he's now 73 and one of the foremost physicists alive — a professor at the University of Cambridge, an investigator of black holes, and the author of the bestselling book "A Brief History of Time."
Here are 15 quotes showing Hawking's approach to science and to life in general.
SEE ALSO: 25 quotes that take you inside Albert Einstein's revolutionary mind
On disability
"My advice to other disabled people would be, concentrate on things your disability doesn’t prevent you doing well, and don't regret the things it interferes with. Don’t be disabled in spirit, as well as physically."
On priorities
"My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all."
["Stephen Hawking's Universe," 1985]
On free will
"I have noticed that even people who claim everything is predetermined and that we can do nothing to change it, look before they cross the road."
["Black Holes and Baby Universes and Other Essays," 1994]
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